One reason to declare constants in multiplicative way, is to improve readability, while the run-time performance is not affected. Also, to indicate, that the writer was thinking in multiplicative manner about the number. Consider this:

double memoryBytes = 1024 * 1024 * 1024;

It's clearly better, than

double memoryBytes = 1073741824;

as the later is not at first glance the third power of 1024.

As Amin Negm-Awad mentioned, the '^' operator is the binary XOR. many languages lack the build - in, compile time exponentiation operator, hence the multiplication.